Merc 500 wont start, Ignition problem?

Nandy

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Apr 10, 2004
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I have a Mercury 500 / 50 H.P. Four motor s/n 2479050 year of manufacture is probably 1968, it has thunderbolt ignition if I recall right.

Short story, I dipped the motor and my transom for less than a minute in the lake. I cleared the carbs from water. With the carbs and the sparkplugs out I shot some mix in to the power head carb holes and the plug holes then cranked the motor. Repeated that procedure a few times until I felt comfortable everything was lubricated. Put it all back, tried to crack the motor but it would crank very hard. As if the starter were not strong enough then the starter died after a couple tries. It really sounded as if the battery was bad, which the voltmeter sais it not and the charger says it was charged before we started working in the motor.

I have started this motor manually before, as recently as maybe not even 2 month ago and it would start manually without much problem. But I too was experiencing trouble getting it to start. When I pull in the rope it start moving then it gets real hard, like the compression was too much. At times it will feel as it kicked back and pull back the string.

I took all the sparkplugs out and did a compression test. All of the cylinders top at 125. Also, without the plugs in it is very easy to turn by hand or with the starter.

I got the rebuilt starter in today but the motor will not start. It will crank fine until I can hear the first combustion, after that it starts to slow down while being cranck. I can also see how the flywheel kicks back at times. I had enough time to take the distributor off and open it up and it was wet. It did not have a pool on it, but it dripped a few drops.

Could that be the reason of the way the motor is behaving? Any input?

Since I have the distributor apart, Should I be doing any maintenance on it?

Thanks!
 

Laddies

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Re: Merc 500 wont start, Ignition problem?

Your engine is hydro locking because it can't compress the liquids and the starter probably has water in it because it was not dried out properly so it don't have the normal amount of torque
 

Nandy

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Re: Merc 500 wont start, Ignition problem?

The starter was rebuilt, new stator, and brushes. I know that one is dry. The hydrolocking theory sounds very interesting, did not thought about it. So, I did empty the carbs, what else do you think I shoudl do to get the water out? Manny thanks for you help.
 

Laddies

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Re: Merc 500 wont start, Ignition problem?

If you have dried the cap and rotor it should start, if it still doesn't turn over with the plugs in you may have to use a little gas to wash the cyls to relieve comp to get it to start
 

Nandy

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Re: Merc 500 wont start, Ignition problem?

IS ALIVE!!! Thanks! After cleaning and drying the distributor it works. I also left the cylinders without sparkplugs to let any water dry.

Thanks for the information.
 

tmcalavy

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Aug 29, 2001
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Re: Merc 500 wont start, Ignition problem?

WD40 is good for drying out damp components. Name means water displacment for 40 days, or so I've heard. Great that you got the beast running again...those are sweet, reliable engines.
 

tmcalavy

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Re: Merc 500 wont start, Ignition problem?

Good thing he didn't get discouraged enough to quit after #39.
 

Laddies

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Re: Merc 500 wont start, Ignition problem?

Your right on that tmcalvay but I wish they would have left the formula alone where you could use it to start a engine with or at lest made it in both formulas
 

Nandy

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Re: Merc 500 wont start, Ignition problem?

Heard that! I think it actually was the propellant they were using before what made it possible to start the motor. But I think it was not safe for the air so they change to the current propellant with seems to be a bit more enviromental friendly.
Thanks!
 
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